Load supporting stands are commercially available for climbing and remaining perched at an elevation upon a tree trunk, utility pole or like structure. Of particularly wide spread use are lightweight portable stands used by hunters which include one or two tree grasping stands.
Such stands have a load supporting platform extending laterally outwardly from the tree trunk and a generally U-shaped member encircling the tree above the level of the platform. The weight of a person supported on a stand creates an eccentric load outward of and generally parallel to the axis of the tree. The eccentric loading is resisted by an equal and opposite force couple which forces the inward portion of the platform toward the tree and creates tensile forces in the U-shaped member forcing that member to grasp the tree. To increase resistance to downward sliding of the platform, engaging means such as a knife edge are conventionally provided on an inward portion of the platform, and such knife edges may also be provided on the inward portion of the U-shaped member.
Typically the stands are carried on a person's back like a knapsack. The stands may be foldable to a compact storage position, or an upper and lower stand may be nested together for ease of transport and storage.
A single stand may be positioned at an elevation by a person climbing the tree possibly with the assistance of commercially available portable ladders, climbing belts, etc. A preferred approach is to use an upper and lower stand which enables a person to climb the tree and provides a seat on the upper stand. Examples of such dual stands are described in the following U.S. Pat. No. 3,960,240 to Cotton issued Jun. 1, 1976; U.S. Pat. No. 4,316,526 to Amacker issued Feb. 3, 1982; U.S. Pat. No. 4,331,216 to Amacker issued May 25, 1982; U.S. Pat. No. 4,417,645 to Untz issued Nov. 29, 1983; U.S. Pat. No. 4,452,338 to Untz issued Jun. 5, 1984; U.S. Pat. No. 4,726,447 to Gibson et al issued Feb. 23, 1984; U.S. Pat. No. 4,953,662 to Porter issued Sep. 4, 1990; and U.S. Pat. No. 4,969,538 to Amacker issued Nov. 13, 1990.
The lower stand conventionally has a generally rectangular load supporting platform, while the upper stand includes an interior opening within which the person stands at approximately waist height during climbing. The upper stand includes a seat and the lower stand often includes foot straps to secure one's feet to the lower stand to facilitate climbing.
The stands are positioned upon the tree trunk and a person stands upon the lower platform within the opening of the upper platform to commence climbing. The upper platform is tilted toward the tree and is lifted with the person's arms. The person then shifts their weight from the lower stand to the upper stand by sitting upon a seat of the upper stand. The lower stand, with all weight removed, is then tilted inwardly and raised by lifting the feet secured by the straps to the lower stand. The process is repeated until the desired elevation is attained and is reversed to the descend from the elevation.
The U-shaped member of conventional stands is commonly a rigid member bolted to brackets on opposing sides of the platform to encompass the tree. A series of bolt receiving holes or telescoping bracket arms enable adjustment to accommodate various tree trunk diameters, and to facilitate rapid installation and removal.
The telescoping bracket arms and associated tree engaging blades represent a significant proportion of the overall weight of the conventional stand. The rigid arms are difficult and awkward to engage with the tree in operation. A disadvantage of such stands is that the width of the platform effectively limits the maximum width of the tree trunk that can be grasped. Enlarging the platform width significantly would result in an undesirable increase in weight. Irregularly shaped tree trunks are not easily accommodated and if such an irregular trunk is not securely grasped by the stand, instability may result.
Since typically the diameter of a tree trunk reduces as one climbs upwardly, the position of the U-shaped member must often be adjusted to maintain the platform in a substantially level orientation. One may readily foresee the consternation of a heavily laiden hunter perched high in a tree, deep in the woods, who drops an essential wingnut, bolt or pin into the surrounding undergrowth. Clearly a high degree of safety and reliability in operation, ease of adjustment and simplicity of design are desirable in such devices.
A tree or pole may be damaged especially by a repeated use of such devices. To alleviate this problem, a stand has also been proposed which utilizes a flexible, flat steel band or strap to function as the U-shaped member encompassing the tree. Such a device is described in United States Patent No. 4,488,620 to Gibson issued Dec. 18, 1984. Neoprene pads are also used on the inward portion of the platform by Gibson to reduce damage.
Damage to the tree is not completely eliminated using such a device since the sharp upper edge of the flexible steel band digs into the tree bark. This embedded edge may be difficult to disengage during climbing rough barked trees, and may penetrate the bark of smooth barked trees.
The steel strap must be flexible enough to allow it to encircle the tree, and to be adjustable in a manner similar to a belt. The steel strap of course must be as lightweight as possible to improve portability. Materials having such qualities would be spring steel or steel strapping, however such materials are prone to brittle fracture. The steel strap may be dented or bent during improper handling and use. Metal fatigue due to continual flexing could lead to sudden brittle fracture and failure of the flexible strap, especially in damaged areas of the strap or areas of stress concentration. Obviously, any fall while hunting in the woods may be significantly more serious than in populated areas. Use of mild steel for the strap would reduce the risk of brittle fracture. However, mild steel is not suitable since it is relatively heavy and is not sufficiently flexible to perform the function.